Recently it was discovered that when selected triaryl phosphites are reacted with chlorine or bromine in an inert organic solvent, intermediate kinetically controlled products are formed, which convert spontaneously at varying rates to the corresponding thermodynamically stable isomers. These newly discovered kinetically controlled triaryl phosphite-halogen compounds have been found to be superior halogenating agents when compared to the corresponding prior art recognized thermodyamically stable products. However, full advantage of the halogenating potential of the kinetically controlled products can only be realized if they are used prior to their rearrangement to the thermodynamically more stable, less reactive, form. Experimentally this has been achieved by preparing the kinetically controlled products at low temperatures immediately before they are utilized in subsequent halogenation reactions. Typically the triaryl phosphite-halogen kinetic compound is prepared in the solvent selected for the desired halogenation reaction; the substrate to be halogenated is then simply added to the resulting solution of the kinetic compound.
The present invention is directed to a method of stabilizing novel halogenating agents. More particularly the present invention is directed to a method of stabilizing the kinetically controlled product of the reaction of chlorine or bromine with a triaryl phosphite of the formula ##STR1## in solution in an inert organic solvent by adding a stabilizing amount of a tertiary amine base or a halide complexing agent.
Use of the present stabilizing techniques allows for the preparation and storage of otherwise unstable halogenating compounds which can be employed in the preparation of known 3-halo-3-cephem antibiotics.